If there were plants inhabiting other planets, which colour would they be? There are no plants in space, but the discovery of exoplanets like Proxima Centaury B or Kepler-442b opens the door for similar organisms that can do photosynthesis. On Earth, plant colours are determined by the type of light emanating from the Sun, our star. In most cases, the best solution has been purple or green colours. In other worlds, with other stars, colours would be completely different.